3,776 research outputs found
Photometric structure of the peculiar galaxy ESO 235-G58
We present the near-infrared and optical properties of the peculiar galaxy
ESO 235-G58, which resembles a late-type ringed barred spiral seen close to
face-on. However, the apparent bar of ESO 235-G58 is in reality an edge-on disk
galaxy of relatively low luminosity. We have analyzed the light and color
distributions of ESO 235-G58 in the NIR and optical bands and compared them
with the typical properties observed for other morphological galaxy types,
including polar ring galaxies. Similar properties are observed for ESO 235-G58,
polar ring galaxies, and spiral galaxies, which leads us to conclude that this
peculiar system is a polar-ring-related galaxy, characterized by a low inclined
ring/disk structure, as pointed out by Buta & Crocker in an earlier study,
rather than a barred galaxy.Comment: 16 pages, 15 figures, accepted for publication in Astronomy &
Astrophysic
Metallicity of the polar disk in NGC4650A: constraints for cold accretion scenario
We used high resolution spectra in the optical and near-infrared wavelength
range to study the abundance ratios and metallicities of the HII regions
associated with the polar disk in NGC4650A, in order to put constraints on the
formation of the polar disk through cold gas accretion along a filament; this
might be the most realistic way by which galaxies get their gas. We have
compared the measured metallicities for the polar structure in NGC4650A with
those of different morphological types and we have found that they are similar
to those of late-type galaxies: such results is consistent with a polar disk
formed by accretion from cosmic web filaments of external cold gas.Comment: Proceeding of the conference "Hunting for the Dark: The Hidden Side
of Galaxy Formation", Malta, 19-23 Oct. 200
Mapping the inner regions of the polar disk galaxy NGC4650A with MUSE
[abridged] The polar disk galaxy NGC4650A was observed during the
commissioning of the MUSE at the ESO VLT to obtain the first 2D map of the
velocity and velocity dispersion for both stars and gas. The new MUSE data
allow the analysis of the structure and kinematics towards the central regions
of NGC4650A, where the two components co-exist. These regions were unexplored
by the previous long-slit literature data available for this galaxy. The
extended view of NGC~4650A given by the MUSE data is a galaxy made of two
perpendicular disks that remain distinct and drive the kinematics right into
the very centre of this object. In order to match this observed structure for
NGC4650A, we constructed a multicomponent mass model made by the combined
projection of two disks. By comparing the observations with the 2D kinematics
derived from the model, we found that the modelled mass distribution in these
two disks can, on average, account for the complex kinematics revealed by the
MUSE data, also in the central regions of the galaxy where the two components
coexist. This result is a strong constraint on the dynamics and formation
history of this galaxy; it further supports the idea that polar disk galaxies
like NGC~4650A were formed through the accretion of material that has different
angular momentum.Comment: 14 pages, 10 figures; accepted for publication in Astronomy &
Astrophysic
Chemical abundances in the polar disk of NGC4650A: implications for cold accretion scenario
The aim of the present study is to test whether the cold accretion of gas
through a "cosmic filament" Macci\`o et al. 2006 is a possible formation
scenario for the polar disk galaxy NGC 4650A. If polar disks form from cold
accretion of gas, the abundances of the HII regions may be similar to those of
very late-type spiral galaxies, regardless of the presence of a bright central
stellar spheroid, with total luminosity of few 10^9 Lsun. We use deep long slit
spectra obtained with the FORS2 spectrograph at the VLT in the optical and
near-infrared wavelength ranges for the brightest HII regions in the disk polar
disk of NGC 4650A. The strongest emission lines ([OII] Hbeta, [OIII], Halpha)
were used to derived oxygen abundances, metallicities and the global star
formation rates for the disk. The deep spectra available allowed us to measure
the Oxygen abundances (12 + log (O/H)) using the "Empirical method" based on
intensities of the strongest emission lines, and the "Direct method", based on
the determination of the electron temperature from the detection of weak
auroral lines, as the [OIII] at 4363 Angstrom. The Oxygen abundance measured
for the polar disk is then compared with those measured for different galaxy
types of similar total luminosities, and then compared against the predictions
of different polar ring formation scenarios. The average metallicity values for
the polar disk in NGC 4650A is Z=0.2 Zsun, and it is lower that the values
measured for ordinary spirals of similar luminosity. Moreover the gradient of
the metallicity is flat along the polar disk major axis, which implies none or
negligible metal enrichment from the stars in the older central spheroid. The
low metallicity value in the polar disk NGC 4650A and the flat metallicity
gradient are both consistent with a later infall of metal-poor gas, as expected
in the cold accretion processes.Comment: 42 pages, 9 figures. Accepted for publication in Ap
Update of High Resolution (e,e'K^+) Hypernuclear Spectroscopy at Jefferson Lab's Hall A
Updated results of the experiment E94-107 hypernuclear spectroscopy in Hall A
of the Thomas Jefferson National Accelerator Facility (Jefferson Lab), are
presented. The experiment provides high resolution spectra of excitation energy
for 12B_\Lambda, 16N_\Lambda, and 9Li_\Lambda hypernuclei obtained by
electroproduction of strangeness. A new theoretical calculation for
12B_\Lambda, final results for 16N_\Lambda, and discussion of the preliminary
results of 9Li_\Lambda are reported.Comment: 8 pages, 5 figures, submitted to the proceedings of Hyp-X Conferenc
VEGAS: A VST Early-type GAlaxy Survey. III. Mapping the galaxy structure, interactions and intragroup light in the NGC 5018 group
Most of the galaxies in the Universe at present day are in groups, which are
key to understanding the galaxy evolution. In this work we present a new deep
mosaic of 1.2 x 1.0 square degrees of the group of galaxies centered on NGC
5018, acquired at the ESO VLT Survey Telescope. We use u, g, r images to
analyse the structure of the group members and to estimate the intra-group
light. Taking advantage of the deep and multiband photometry and of the large
field of view of the VST telescope, we studied the structure of the galaxy
members and the faint features into the intra-group space and we give an
estimate of the intragroup diffuse light in the NGC 5018 group of galaxies. We
found that ~ 41% of the total g-band luminosity of the group is in the form of
intragroup light (IGL). The IGL has a (g - r) color consistent with those of
other galaxies in the group, indicating that the stripping leading to the
formation of IGL is ongoing. From the study of this group we can infer that
there are at least two different interactions involving the group members: one
between NGC 5018 and NGC 5022, which generates the tails and ring-like
structures detected in the light, and another between NGC 5022 and
MCG-03-34-013 that have produced the HI tail. A minor merging event also
happened in the formation history of NGC 5018 that have perturbed the inner
structure of this galaxy.Comment: 21 pages, 15 figures. Accepted for publication in Ap
Incidence of temporomandibular joint clicking in adolescents with and without unilateral posterior cross-bite: a 10-year follow-up study
Among different malocclusions, posterior cross-bite is thought to have a strong impact on the correct functioning of the masticatory system. The association between unilateral posterior cross-bite (UPCB) and temporomandibular joint (TMJ) clicking, however, remains still controversial. The aim of this study was to investigate whether the presence of UCPB during early adolescence increases the risk of reporting TMJ clicking after a long-term follow-up. A longitudinal survey design was carried out in a group of 12-year-old young adolescents, who were examined at baseline for TMJ clicking sounds and unilateral posterior cross-bite. After 10 years, 519 subjects could be reached by a telephone survey. Standardised questions were used to collect self-reported TMJ sounds and to determine whether participants had received an orthodontic treatment. Logistic regression analysis revealed a significant association between unilateral posterior cross-bite and subjectively reported TMJ clicking (odds ratio = 6·0; 95% confidence limits = 3·4-10·8; P < 0·0001). The incidence of TMJ clicking was 12%. At a ten-year follow-up, self-reports of TMJ clicking were significantly associated with the presence of UPCB at baseline, but not with the report of having received an orthodontic treatment. Within the limitation of this study, the presence of unilateral posterior cross-bite in young adolescents may increase the risk of reporting TMJ sounds at a 10-year follow-up. The provision of an orthodontic treatment, however, does not appear to reduce the risk of reporting TMJ sounds
The Fornax Deep Survey with VST. I. The extended and diffuse stellar halo of NGC~1399 out to 192 kpc
[Abrigded] We have started a new deep, multi-imaging survey of the Fornax
cluster, dubbed Fornax Deep Survey (FDS), at the VLT Survey Telescope. In this
paper we present the deep photometry inside two square degrees around the
bright galaxy NGC1399 in the core of the cluster. We found a very extended and
diffuse envelope surrounding the luminous galaxy NGC1399: we map the surface
brightness out to 33 arcmin (~ 192 kpc) from the galaxy center and down to
about 31 mag/arcsec^2 in the g band. The deep photometry allows us to detect a
faint stellar bridge in the intracluster region between NGC1399 and NGC1387. By
analyzing the integrated colors of this feature, we argue that it could be due
to the ongoing interaction between the two galaxies, where the outer envelope
of NGC1387 on its east side is stripped away. By fitting the light profile, we
found that it exists a physical break radius in the total light distribution at
R=10 arcmin (~58 kpc) that sets the transition region between the bright
central galaxy and the outer exponential stellar halo. We discuss the main
implications of this work on the build-up of the stellar halo at the center of
the Fornax cluster. By comparing with the numerical simulations of the stellar
halo formation for the most massive BCGs, we find that the observed stellar
halo mass fraction is consistent with a halo formed through the multiple
accretion of progenitors with a stellar mass in the range 10^8 - 10^11 M_sun.
This might suggest that the halo of NGC1399 has also gone through a major
merging event. The absence of a significant number of luminous stellar streams
and tidal tails out to 192 kpc suggests that the epoch of this strong
interaction goes back to an early formation epoch. Therefore, differently from
the Virgo cluster, the extended stellar halo around NGC1399 is characterised by
a more diffuse and well-mixed component, including the ICL.Comment: Accepted for publication in ApJ; 25 pages and 14 figures. An higher
resolution file is available at the following link
https://www.dropbox.com/s/fvltppduysdn6pb/NGC1399_fin_2c.pdf?dl=
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